The present invention relates to a method of applying a bonding paste to a substrate.
In a die bonding for bonding chips to a substrate such as a lead frame, a paste for bonding is applied on the substrate. A dispenser moves an application nozzle from which a paste is discharged, and applies the paste in an application area on the substrate. In this method, a moving route of the application nozzle from the application start point to the application terminating point in the application area is set. The area is determined according to the shape of the chip. The moving route is defined in various shapes depending on a pattern of the route. For example, the paste is applied in a rectangular area, for example, along a cross-shape where the application nozzle moves in an X-figure, or along an asterisk-shape where a plus (+)-figure is overlapped on the X-figure.
A conventional application method will be explained below with reference to FIG. 4.
FIG. 4 shows a conventional application track of the paste. Within an application area A, a drawing pattern has an asterisk-shape. The application nozzle starts applying the paste from the drawing center C toward the outside, and then moves radially while commuting between turning points T1, T2, T3, . . . set near the center C, and end points P1, P2, P3, . . . set respectively at ends of application lines. The nozzle moves along all application lines, and applies the paste along the specified asterisk shape.
However, moving the application nozzle along the complicated application pattern such as the asterisk shape by a single stroke has the following problems. Whenever moving back and forth between the drawing center and each end, the nozzle must once stop at the turning points T1, T2, T3, . . . set near the center in order to change the direction. Accordingly, the application nozzle must decelerate and accelerate very frequently, such that the cycle time of the entire application operation is extended and the application efficiency is lowered. Furthermore, an average speed near the drawing center is lower than that in other areas, and the nozzle accordingly stays near the center for a longer time. As a result, the paste is applied around the center more and thus is not applied uniformly.
An application method for applying a bonding paste according to the present invention has an enhanced application efficiency and applies the paste uniformly.
The method of applying a bonding paste on a substrate uses an application nozzle moving and discharging the paste along a drawing pattern having a cross shape where plural application lines cross. The method includes:
(a) a step of moving the application nozzle from the application start point set near the center of the cross shape to a first end point on a first application line of the plural application lines,
(b) a step of moving the application nozzle from the first end point to a second end point of the first application line along the first application line,
(c) a step of moving the application nozzle from the second end point to a first application terminating point set near the central position of the first application line along the first application line,
(d) a step of moving the application nozzle from the first application terminating point to a third end point on a second application line of the plural application lines along the second application line,
(e) a step of moving the application nozzle from the third end point to a fourth end point of the second application line along the second application line, and
(f) a step of moving the application nozzle from the fourth end point to a second application terminating point set near the central position of the second application line along the second application line.
In this method, the application nozzle stops near the center less frequently, has a shortened cycle time, and applies the paste uniformly.